Continuing pipe operator in Query.jl standalone query operators

General Usage
1

In Query.jl I can easily continue the pipe in a LINQ style query via parenthesis in the @query macro, for instance like this:

df = DataFrame(name=["John", "Sally", "Kirk"], age=[23., 42., 59.], children=[3,5,2])

@pipe df |> @query(i, begin
            @where i.age>50
            @select {i.name, i.children}
            end) |>
          DataFrame |>
          first(_)

My question now is how can I continue a pipe with the standalone operators; the following, of course, does not work.

@pipe df |> @groupby(_.a) |> @map({a=key(_), b=mean(_.b)}) |>
@filter(_.b > 5) |> @orderby_descending(_.b)  |>
DataFrame |> first(_)

I would like to have a solution since I understood that most of the new features in Query.jl are coming for the standalone syntax.